Seeker system



March 12, 1963 E. F. LAFHAM, JR., ET AL SEEKER SYSTEM March l2, 1963 E. F. LAPHAM, JR., ETAL 3,081,050

SEEKER SYSTEM Filed April 27, 1954 5 Sheets-Sheet 2 IN VEN TORS /A/V H. Mc LAREN wmd-Mw vT foMwvo E Af/MM JR.

March 12, 1963 E. F, LAPHAM, JR., ETAL 3,081,050

SEEKER SYSTEM Filed April 27, 195A 5 sheets-sheet 3 15% A V V E 5 INVENTORS EDMUND F. APHAM JR BY /A/V H. Mc LAREN 3,081,050 SEEKER SYSTEM Edmund E'. Lapham, 5r., Birmingham, and ian H. Mc- Laren, Dearborn, Mich., assignors to The Bendix Corporation, a corporation of Delaware Filed Apr. 27, 1954, Ser. No. 4%,644 9 Claims. (Cl. 244-14) This application is a continuation in part of copending application Serial No. 175,442 filed July 22, 195() by Edmund F. Lapham, Jr. and lan H. McLaren and now abandoned and co-pending application Serial No. 188,943, filed October 7, 1950 by Edmund F. Lapham, Ir.

This invention relates to a system for, and method of, guiding a missile toward a target. More particularly, the invention relates to a seeker system for so guiding a missile on a collision course toward a target that the missile will intercept the target regardless of the flight path which the target adopts. The invention also provides a method of guiding the missile on a collision course to intercept a target.

There are, in general, two basic ways in which a missile may be guided to intercept a target. As one alternative, the missile may be guided by a launching aircraft on the basis of information which the aircraft receives from the target. This indirect method of controlling the missile requires the launching aircraft to remain in the vicinity of the target during the flight of the missile. This is dangerous if there are any hostile aircraft nearby. Furthermore, such a system usually does not have suicient sensitivity, preventing the flight of the missile from being accurately controlled.

Instead of having the launching aircraft guide the missile, the missile may be allowed to guide itself. The missile may be provided with transmitting equipment and an antenna for sending signals to the target. These signals may then be reflected from the target to the missile antenna and utilized by the missile to vary the direction of its flight. This direct method permits the direction of missile flight to be corrected within a minimum time after the missile has deviated from its true course. It also permits the missile to be independent of the launching aircraft once it is in flight.

Assuming that the missile guides itself, there are various courses which it may follow in approaching a target. -As one possibility, the missile may proceed on a path substantially perpendicular to the path of the target until it crosses the target wake. The missile would then turn sharply so as to follow the wake of the target until it in,- tercepts the target. This course is disadvantageous because of the excessively high accelerations required to abruptly turn the missile when it crosses the targets wake. Furthermore, the control exerted on the missile would be at a minimum between the time the missile is launched and the time it crosses the targets wake. Because of this, the missile might cross a wake belonging to an object other then the target and might intercept the wrong object.

The missile might also follow a homing course in which the missile would always point directly toward the target. This course would require the missile to make sharper and sharper turns as it approaches the target, especially when the target is following a sharply curved path itself. As a result, the lateral accelerations which the missile must meet in order to hit the target are far greater than a practical missile can perform and it would sometimes miss the target by relatively large distances.

It has also been suggested that the missile be made to point ahead of the target so that if the missile and target continue on their respective courses, they will collide. This course is accurate only if the target follows a straightline path at constant speed, and considerable errors are 'ice introduced if the target follows a curved path or if its speed varies.

The course which is followed by the missile in this seeker system has none of the above disadvantages. In this system, the missile has an antenna which is pointed directly at the target before the missile is released. A line of sight is therefore formed between the antenna and the target and this line of sight is maintained after the missile is released. In other words, the missile gradually gains on the target in the direction of the line of sight while maintaining the same velocity as the target in directions perpendicular to the line of sight. This causes the missile to intercept the target whether or not the target follows a straight or curved path.

An object of this invention is to provide a system for controlling the course of a missile so that it will always intercept a moving target.

Another object is to provide a system of the above indicated character which may be installed in the missile itself.

Another object is to provide a seeker system of the above indicated character for guiding a missile to intercept a target regardless of the path which the target may be following.

A further object is to provide a seeker system of the above indicated character for guiding a missile to intercept a target without imposing excessive lateral or forward accelerations upon the missile.

Still another object of this invention is to provide a system of the above character which is simple, efficient and reliable.

A still further object of this invention is to provide a system of the above character which will occupy a minimum amount of space so that the missile itself may carry a maximum amount of explosive material.

Another object of the invention is to provide a method for guiding a missile to intercept a target regardless of the ight path which the target may be following.

Other objects and advantages of the invention will be apparent from a detailed description of the invention and from the appended drawings and claims.

In the drawings:

FIGURE 1 is a block diagram of an electrical system for guiding a missile to intercept a target;

FIGURE 2 is a perspective View of the missile which carries the system shown in FIGURE 1;

FlGURE 3 is an enlarged perspective view of the antenna which is used in the system shown in FIGURE 1;

FIGURE 4 is a diagrammatic view of the beam transmitted by the antenna shown in FIGURE l;

FIGURE 5 is a view of the positions of the missile and the target at any instant, showing the courses which the missile and target are following at that instant;

FIGURE 6 illustrates a course taken by the missile to intercept the target when the target is following a particular path;

FIGURE 7 illustrates voltage curves at strategic points in the modulator of the system shown in FIGURE 1;

FIGURE 8 shows the pattern of the signals reflected by the target when the missile deviates from a proper collision course;

FIGURE 9 illustrates the pattern of the signals reflected by the target with respect to each of four quadrant signals when the missile deviates from a proper colli-sion course, the signals in opposite quadrants being combined to produce a pair of resultant signals for correcting the course of the missile; and

FIGURE l0 is an enlarged rear elevational view of the missile tail fins, showing the angle of missile rotation for which compensation must be provided by the system shown in FIGURE l before the course of the missile can be corrected.

Collision Course Guidance Theory In the ideal collision course, the true bearing of the line of sight from the missile to the target remains fixed in'space during the flight. FIGURE 5 illustrates the collision course which a missile, generally indicated at 10, follows at any instant toV intercept a target, generally indicated at 11. The missile has at any instant a velocity VM and the target a velocity VT. The velocity VM may beV resolved into components Vmm, VM), and VM@ along the axes of a coordinate system in which thearus VM@ coincides with a line of sight 12 between the missile and the target. Similarly, the velocity VT of the targetV may be resolved into components VTM), VTQ), and V'T), which are parallel to the above coordinates. In a collision Since the only relative motion is along the line of sight 12, the. missile moves toward the rtarget 11 with a velocity VmDU-VTQ) and ultimately intercepts the target.

The course ofthe missile for a particular flight path of the target 11 is illustrated in FIGURE 6. it will be seen that the line, of sight 12 remains fixed and that the length of this line gradually decreases as the missile overtakes the target.

Missile Construction The missile has a cylindrical body, generally indicated at 1,4 (FIGURE 2), and an antenna, generally indicated at 15 (FIGURES 2 and 3). The body 14 holds the electij-ical system for guiding the missile as well as an explosive charge which is detonated when the missile intercepts the target 11. A first pair of diametrically disposed hns 17 and a second pairof diametrically disposed fins 18 having a 9K0"l phase relationship with respect to the fins 17 are attached to the missile at an intermediate position in the missile. Each of the ns 17 and 13 may be a suitably shaped at strip of material which is pivotably secured to` the body 14. The position of the fins 17 determines the direction which the missile follows in one plane and the position of the fins 18 determines `the direction of the missile flight in a second plane substantially perpendicular to the first plane.

Before the missile is launched, the antenna is electrically coupled tothe antenna of a radar system in the launching airplane. This radar system is employed to locate the target and to train the antenna on the target. During this time, the body 14 of the missile is held in a fixed position on the launching aircraft but the positions of the fins 17 and 18 may be adjusted by the missile system, which may be operated even while the missile is caged. Since the position of the body 14 is fixed before flight, the missile will probably be launchedwith an initial error. However, Vbecause of the position of the fins 17 and 18, the missile will start to turn, immediately after it is released, in the proper direction to intercept the target. The missile will not be launched if it has to turn through an excessive angle to intercept the target, such as an angle greater than 30.

Transmitter In one embodiment of the invention, pulses recurring at a predetermined frequency are provided to modulate a carrier wave and the resultant signals are beamed toward the target. The pulses are obtained from a moduiator which includes a power source 20, a high voltage transformer 21, a differentiating transformer 22, a trigger circuit 23, a switch 24, a pulse forming network 25 and a pulse transformer 26. The input side of the transformer 21 is connected to the power source 2t) and the output is connected between the input winding of the transformer 22 and a terminal 27 connected to the switch 24. The other side of the input winding of the transformer 22 is grounded and the output winding of the transformer 22 is connected between the input side of the trigger circuit 23 and ground. The output side of the trigger circuit 23 is connected to a terminal 30 of the switch 24. The switch 24 may be a thyratron tube with its plate connected to the terminal 27, its cathode connected to the terminal 28, and its grid connected Vto the terminal 3i). The pulse forming network 25, which may have a capacitive reactance at the frequency of the power source 2&3, is connected between the terminal 27 and the input winding of the pulse transformer 26, one side of which is grounded. The output winding of the pulse transformer is connected to a magnetron 33 and the output signals from the magnetron 33 are introduced through an ATR (anti-transmit-receiver) switch 34 to the antenna 15.

The voltage from the power source Ztl is stepped up by the power transformer 21 before being applied to the switch 21.3 and pulse forming network 25. The switch 24 is normally open and is closed only when a triggering pip is introduced to its grid terminal 30. The triggering pip is formed by `a current which flows through the output winding of the transformer 21 and the input winding of the transformer 22. The ytransformer 22 has a magnetic core which has relatively large inductance for small currents and a low inductance for large currents. As is well known, the voltage induced in a transformer is proportional to Ldi/dt, where L is the inductance and d/dt is the rate of change of current. Since L and oli/dt are relatively large in the transformer 22 for small values of current and decrease rapidly as the sine wave current in the transformer approaches its peak, the voltage induced in the transformer has a pip at zero'current. This pip is amplified by the trigger circuit 23 and is then applied to the terminal 3@ of the switch 24 s o as to cause the switch to close.

During the intervals between the closingV of the switch 24, the network 25 is charged to a high value through a series resonant circuit which includes the secondary winding of the transformer 21, the network, the primary winding of the pulse transformer 26 and the primary winding of the differentiating transformer 22. The network 25 is charged to a maximum value at substantially the same time that the tube 24 starts to conduct, as disclosed in Patent N o. 2,674,691 issued April 6, 1954, to Stanley J. Krulikoski, Jr., et al. When the switch 24 closes, it provides a discharge path of relatively low impedance for the network 25, causing the network to discharge in a relatively short and heavy pulse through the switch 24 and the pulse transformer 26. The transformer 26 steps up the voltage of each discharge pulse before introducing it to the magnetron 33, the oscillations of which provide carrier signals for the pulse. The signals are then introd uced through the ATR switch 34 to the antenna 15 for transmission toward a target such as the target 11 shown in FIGURES 5 and 6. The impedance of the ATR. switch is short circuited by the output from the magnetron during the transmission periods so that the antenna is effectively connected directly to the magnetron. At other times, the switch is operi to prevent received signals from being introduced to the magnetron and modulator.

The wave forms at the Various components of the modulator, and their relative phases, are shown in FIGURE 7. Curve 36 shows the shape of the voltage pips which are developed in the transformer 22 when the current through the transformer is passing through zero. Curve 38 illustrates how the voltage across the network 25 builds up during the charging period and how the voltage falls when the switch 24 closes upon the introduction of the amplified voltage pips from the trigger circuit 23. Curve 39 illustrates the shape of the pulses formed in the transformer 26 by the discharge of the network 25 and also shows the phase relationship of these pulses to the pips developed by the transformer 22. Curve 40 is an enlarged diagram of one of the pulses shown in curve 39.

A ntenna a mount gimbal 41 (FIGURE 3), a ring gimbal 42, a horseshoe gimbal 43, and a reiiector 44. The mount gimbal 41 is adapted to rotate with respect to the missile in a plane perpendicular to the axis of the missile. The ring gimbal 42 is mounted between a pair of diametrically opposed uprights 45 which extend from the mount gimbal, and is adapted to pivot with respect to the mount gimbal. The horseshoe gimbal 43 is mounted for pivotal movement on the ring gimbal and the reflector 44 is in turn mounted for rotary movement on a shaft '46 which is secured to the horseshoe gimbal. The reflector has the shape of a paraboloid, the axis of which is slightly offset with respect to the axis of the shaft `46. Extending from and forming a part of the refiector 44 is a hollow cylindrical portion 47. A motor positioned within the cylindrical portion 47 operates to drive the `cylindrical portion and the reector at a particular speed, such as 180 revolutions per second. Because of this relatively high speed of rotation the cylindrical portion 47 and the refiector 44 serve as a free gyro unit and the reiiector maintains a fixed reference even though the missile may pivot with respect to the refiector.

The refiector 44, being a paraboloid, transmits a relatively narrow directional beam. Since the axis of the reflector is slightly offset with respect to the axis of the shaft 46, this directional beam rotates in accordance with the rotation of the reflector. Therefore, for each complete revolution of the reflector, the beam describes a cone 48 (FIGURE 4) in space. This cone has an axis 49 which serves as the center of circularcross sections, such as the cross section 50, taken perpendicular to the axis. The beam 51 from the reflector rotates about the circle 50 as the reflector turns through a 360 arc.

When the target 11 lies on the axis 49, it will be in a region of constant intensity relative to the beam 51 as the beam rotates. Movement of the target t0 a position 53 -which is displaced from the axis 49 will cause the strength of the beam on the target to vary in a pattern approximating a sine wave as Vthe reiiector 44 rotates through a 360 arc. The sinusoidal pattern is formed because the signal strength of the echo increases as the center of the beam approaches the target and decreases as it moves away from the target.

The relative phase of the sinusoidal pattern indicates the direction of the target from the scan axis. For example, the phase of the pattern when the target is at position 53 will be different from the phase of the pattern when the target is at position 54. Furthermore, the amplitude of the sinusoidal pattern will increase as the target moves radially outwardly from the conical axis 49. Curves 55 and 56 (FIGURE 8) illustrate the pattern of the reflected signals when the target is at positions 53 and 54, respectively. Both curves have an approximately sinusoidal shape but their phase and amplitude differ because of their different positions relative to the axis 49.

The position of the fins 17 and 18 (FIGURE 2) are adjusted in accordance with the amplitude and phase of the sinusoidal pattern, as will be described in detail hereinafter. By adjusting the position of the fins, the body 14 of the missile pivots about the antenna 1S in a direction to change its course, so that the target will once again appear on the `axis 49 of the conical beam 48.

The missile may pivot either on the ring gimbal 42 or on the horseshoe gimbal `43 in order to correct its course. However, the missile is so constructed that the refiector 44 strikes the rig gimbal 42 after the missile has rotated through a relatively limited angle on the horseshoe gimbal 43. To prevent the reflector from ever striking the ring gimbal, the movement of the missile on the horseshoe gimbal is converted into a rotation of the mount gimbal 41. As the mount gimbal 41 rotates, the ring gimbal 42 rotates with respect to the missile in a compensatory motion. By having compensatory movements in two substantially perpendicular planes, the flight of the missile can be corrected without any movement in a third plane substantially perpendicular to the first two planes. As a result, the horseshoe gimbal 43 always remains substantially perpendicular to the ring gimbal 42. The operation of the antenna 15 in converting movements of the missile relative to the horseshoe gimbal 43 into a rotation of the missile relative to the mount gimbal 41 and a compensatory pivotal movement of the missile relative to the ring gimbal 43 is fully disclosed in co-pendng application Serial No. 188,943, filed October 7, 1950', by Edmund F. Lapham, Ir.

Receiver The receiver includes a balanced mixer 62 (FIGURE 1), a local oscillator 64, a detecting circuit, an automatic frequency control circuit, and an automatic gain control circuit. The mixer `62 is connected through a TR (transmit-receive) switch 60 to the antenna 15. The local oscillator 64, which may include a reflex oscillator Klystron tube, is also connected to the mixer 62 and has a frequency which differs from the frequency of the oscillations of the magnetron 33 by an intermediate frequency, such as a frequency of I.F.

The detecting circuit includes an intermediate frequency amplifier 66, a crystal detector 63, a video amplifier and a cathode follower 72. The intermediate frequency amplifier 66, which may include a plurality of stages, is connected to the output side of the mixer and its output is in turn introduced to the detector 68. The video amplifier 70 and the cathode follower 72 are in series with detector 68.

The automatic frequency control circuit includes an intermediate frequency amplifier 76, a discriminator 78, a video amplifier 8f) anda multivibrator 82. The amplifier 76 is connected to the mixer 62 and is in turn connected to the discriminator 78. The output from the discriminator 78 is introduced to the amplifier 80, and, after being amplified and detected, it is fed into the multivi- Ibrator 82. The output side of the multivibrator 82 is connected to the input side of the local oscillator `64.

The input side of the automatic gain control detector '74 is connected to the output side of the intermediate frequency amplifier 66. The output of the detector 74 is `fed back into the amplifier to maintain the output of the amplifier constant.

The signals transmitted by the antenna -15 are refiected by the target 11 and received back at the antenna after a time interval dependent upon the distance between the antenna and the target. The received signals then pass through the TR switch 60 into the mixer 62. During the periods of pulse transmission, the TR switch 60 reduces the strength of the signals which pass into the receiver Ito prevent the transmitted pulses from paralyzing the receiver. At all other times, the switch permits signals to pass directly to the mixer without any loss.

The received signals are mixed in the mixer 62 with the signals from the local oscillator 64 to produce beat frequency signals. These beat frequency signals are amplified and detected by the intermediate frequency amplifier 66, the detector 68, the video amplifier 70 and the cathode follower 72. 'The amplifier 66 is gated so that a received signal passes through the amplifier only at the time the echo is expected from the target 11. Gating is accomplished by supplying a pulse voltage rather than a continuous voltage to the plate of the last LF. stage. The pulse is supplied through a lead 84 from a range gate circuit hereinafter to be described.

In order to maintain an intermediate frequency of LF., the Vfrequency of the local oscillator is controlled by sample signals which are introduced from the magnetron 433 through the mixer 62 to the amplifier 76. These signals are mixed with signals from the local oscillator 64 to give intermediate beat frequency signals having a frequency of approximately LF., which are introduced to fthe discriminator `78. The discriminator is so designed that its output becomes positive for beat frequency signals having a frequency above LF. and negative for signals having a. frequency below LF. When the signal Ifrom the discriminator 'i8 is positive, the output of the oscillator 64 increases and the resultant increase in heat distorts the configuration of the cavity in the oscillator tube so as to cause the oscillation frequency to decrease. Likewise, a negative signal from the discriminator causes the output of the oscillator to decrease and consequently its` frequency to increase. As a practical matter, the power of the oscillator increases and decreases so rapidly Ithat the frequency of the oscillator drifts a negligible amount from the desired intermediate frequency. This intermediate frequency is maintained even though the frequency of ythe magnetron 33 may change as a result of drifts in its thermal characteristics.

In addition to frequency compensations, the strength of the received signals must be compensated so that the signals will remain within certain levels. This compensation is necessary because the strength of the signals received from the target varies inversely with the distance between the missile and the target. The automatic gain detector 74 is provided to cut down on the strength of the received signals when the target is close to the missile and Ito increase the strength of the signals when the target is somewhat distant from the missile. The detector does not affect in any way the amplitude of the sinusoidal envelope which is produced when the target is off the axis 49 of the cone 48 traced by the antenna beam.

Range Gate The range gate unit permits the seeker to fixV on only one target, such as the target 411, and eliminates from consideration other targets having different ranges than the target being pursued. The gate unit includes avariable range multivibrator 90, an early gate generator 96, a late gate generator 100, and two gated amplifiers 104 and 106 associated with the gate generators 96 and y100, respectively, The input side of the variable range multivibrator 90 is connected to the output side of the trigger circuit 23, and the output side of the multivibrator is connected to a differentiating network 92. The differentiating network 92 is connected to an amplifier 94, the output from which is introduced to the early gate generator 96 and through a delay line 98 to the late gate generator 100. Signals from the generators 96 and 100 are mixed in a gate amplifier and mixer 102 and the resultant signal is fed `through the lead 84 to the intermediate frequency arnplifier 66, as previously explained. Signals from the generators 96 and 100 are also introducedto the gated amplifiers 104 and 106 respectively, where they are mixed with received pulses supplied through leads 108 and 110 from the cathode follower 72. The output from the gated amplifier 104 is introduced through an integrating diode 112 to a cathode follower 116 and is mixed in the cathode follower with the signalsV passing from the -gated amplifier 106 through an integrating diode 11,4. The output side ofthe cathode follower is connected to the input side of the variable range multivibrator 90.

The multivibrator 90 -istripped by trigger signals from the trigger circuit 23. These pulses are similar :to the signals which close the switch 24 in the modulator. After the multivibrator operates for a period of time determined by the bias from the cathode follower 1116, as will be explained hereinafter, it trips 'back and produces a voltage change. This voltage change is differentiated by the differentiating network'92 -to form Va positive pulse which is vamplified and then used to trigger the early gate generator 96. The pulse also triggers the late gate generator 100 after a fixed amount of time determined by the constants of the `delay line 98. The pulses formed by the generators 96 and 100 are approximately 1A micro- 'Second long and are mixed in rthe amplifier and mixer 102 before being introduced through the lead `84 to the plate of the amplifier 66. Y

Ars previously explained, the -amplier 66 permits the signals received by the `antenna 15 to pass only at the times, that pulses. `are Supplied through the, lead 84 Therefore, in order for the system to function properly, pulses supplied through the lead 84 must coincide in time'with'the signals reflected from the target 11. This proper timing is provided -by the gated amplifiers 104 yand 1016. The gate signal from the generator 96 is mixed in the amplifier 104 with-the vi-deo signal 4from the cathode follower 72, and the gate Afrom the gener-a- -tor and the video signal are mixed in the amplifier 106. An output signal is obtained only when the gated and video signals'are introduced to an amplifier at the same time. Therefore, the outputs from the `ampliers 104 and i106 consist of portions Yof the video signal which occur lduring the respective early and ylate gates. These outputs are integrated by Ithe diodes 112 and 114 and yapplied to the cathode follower Y116 in such a manner that the output `from the diode 112 raises the grid voltage of the cathode 4follower and the output vfrom diode 1,14 lowers the grid voltage. The resultant grid voltage controls the output of the cathode follower. Since the output of `the cathode follower is applied to the input of the multivibrator 90, it controls the time at which the multivibrator trips back or, in other words the time at which the range gate is produced. Thus, if 4a larger yfraction of the target echo signal liesl in the early Igate, the voltage fed to the cathode follower ywill inc-rease. This in turn increases the voltage on the grid of the range multivibrator 90 and produces a delay in the time at y*which the next range gate pulse occurs. As a result, the target echo is centered between the pulses of the generators 96 and 100 and the amplifier 66 is triggered only when the target echo is received.

The Comparator To obtain information on the position of the target, the conical scan of the reflector is divided into quadrants corresponding to up, down, right, and left positions. This .is accomplished fby a two-phase alternator and tran-sformers 122 and i124 connected to thealternator. The alterna-tor is directly coup-led to the vantenna. reflector 44 and produces two sine wave signals which are 90 out of phase lwith each other. One of these signals is fed into the center-tapped `transformer 122 which subdivides the -signal int-o two signals 180 out of phase with each other. In like manner, the center-tapped transformer I124 subdivides the second signal into two signals 180 out of phase with each other. The four resultant signal-s have a quadrant relationship. l v

The positive half of each quadrant signal is employed to gate one of the gate amplifiers 126, 128, 130 and 132. Video signals from the cathode follower 72 are also introduced through a lead 1'34 to the amplifiers 126,128, and .132, where they are mixed with the signals from the transformers. The outputs of the amplifiers are separately detected by four peak detector circuits 136, 13,8, 1,40 and 142, respectively, and `fed to the grids of four cathode followers 144, 146, 148` and I150,'respectively. The detectors Iare provided with a Vrelatively long time constant so as to eliminate the effects of noise and other undesirable signals. Y Y i Since the alternator 120 is coupled to the antenna each gate corresponds to of antenna rotation. The gate signal introduced to the amplifier 126`is phased to permit lpulse signals to pass during the time that the antenna beam is scanning through the top half of 4the cone 48. Likewise, the gate signal introduced to the amplifier 128 is phased to pass pulsesignals during the time that the antenna beam is rotating through the bottom half of the conical cone 48. The amplifiers 130 and 132 pass signals which are received while the antenna is rotating through the left `and right halves of the cone, respectively. i

The .strength of Ithe echo pulses which are introduced to the different gates depends upon the position of the target in the conical scan. For example, if the target is on the axis 49 of :the scan, the amplitude of the pulses will be the same for each gate. If the missile has to be turned upwardly to proceed on a proper course, the strength of the output signal from the gate controlling `the upward movement is greater than the strength of the output signal from the gate controlling the downward movement. By combining the two signals, :a resultant error signal is produced. Thus, the signals :from the gate ampliflens 126 and 12S are combined in a signal resolver -152 to determine movement in the vertical direction, and the signals -from 4the, amplifiers 130 and 132 are combined in a resolver 154 to determine movement in 4the horizontal direction.

The curves in FIGURE 9 indicate the relative phases of the different gate signals and the strength of the pulses reilected from a target in position 53 as lthe reflector 44 rotates through a 360 arc. The `gated signals introduced .to the ampliers 126, 128, 136 and 132 are indicated at :156, 157, 158, and 159, respectively, and Ithe pattern of the retlected pulses is indicated at 160, 161, 162 and l163, respectively. Since `the target is off the axis 49 of the conical scan 48, the amplitude of the pulses rellected from the target varies in an approximately sinusoidal pattern as the reflector rotates through a 360 arc. With the target in the position l53, the peak `signals passing through the amplifiers 126 and `13d) eX- ceed the peak signals passing through the ampliers 12S and `132, respectively. The direction in which the mi sile is headed is therefore changed upwardly and to the right.

Signal Resolver and Dz'fjferentz'ator As previously explained, when the course of the missile is in error so that the target is no longer on the axis 49 of the conical scan 4S, the ns 17 and 18 are pivoted. This causes the missile to turn with respect to the antenna, thereby altering its course to provide the necessary correction. However, the missile can turn through only a limited angle on the horseshoe gimbal 43 before the reflector 44 strikes the ring gimbal 42. Therefore, any tendency for the missile to pivot on the horseshoe gimbal is converted into a rotation of the missile on the mount gimbal 41. When the missile rotates on the mount gimbal, the axes formed by the ns 17 and 18 become displaced with respect to the axes of the reflector 44. In order to correct for subsequent deviations in the course of the missile, the error signals as determined by the reference axes of the rellector 44 must be shifted by a phase angle corresponding to the angle of rotation of the missile on the mount gimbal. FlGURE l indicates the angle 164 through which the missile has rotated on the mount gimbal at any instant. The initial position of the missile ns 17 and 13 is shown in broken lines and the position of the fins after the rotation of the missile through the angle 164 is shown in solid lines.

Signal resolvers 152 and 154 are provided to change the reference axes of the error signals by the angle 164 through which the missile has rotated With respect to the mount gimbal 41. The resolvers may be square card sine potentiometers having variably positioned taps connected to the mount gimbal.

In order for the missile to proceed on a collision course toward the target-ie., along the line of sight 12-the error signals from the signal resolvers are differentiated by dilerentiators 170 and 172, respectively. The differentiators 170 and 172 provide signals the strength of which are dependent upon the distance of the target from the axis 49 of the cone 48. When the missile has deviated a considerable distance from its correct course, the signals provided by the differentiator are strong but, when the deviation is slight, the dilferentiator signals are weak. In this way, the ditferentiators prevent the missile from oscillating excessively from one side to the other of the axis 49 and in effect provide the missile with damped harmonic oscillatory movements which cause deviations in the flight l@ of the missile to be corrected in a minimum amount of time.

The signals from the diiferentiators 170 and 172 may be introduced directly to servomechanisms 174 and 176, respectively, or they may be combined with the output from the resolvers 152 and 154, respectively, -as indicated by the broken lines, before they are introduced to the servomechanisms. The servomechanisms 174 and 176 are connected to the fins 17 and 18, respectively, to alter the position of the fins. As previously explained, the position of the ns is altered to pivot the missile about its antenna so that its direction of llight is corrected.

Although this invention has been disclosed `and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art.

What is claimed is:

1. In combination in a seeker system for guiding a missile to intercept a target, means for producing pulses of high frequency energy recurring at a predetermined lower frequency, an antenna for beaming these pulses to a target in a revolving pattern, the antenna also serving to receive the signals reected from the target, means including four gated ampliers for producing four signals out of phase with one another, the received signals being introduced to the ampliers to vary the output of the -ampliers, means for combining the output .amplifier signals of opposite phase to produce a pair of error signals 90 out of phase with each other, means `for shifting the phase of the error signals to compensate for movements of the missile relative to the antenna, and means for adjusting the positioning of the missile relative to the antenna in accordance with the phase shifted error signals to correct any deviations in the ight of the missile from a collision course towards the target.

2. In combination in a seeker system for guiding a missile to intercept a target, means for producing a high frequency carrier wave, means for modulating the carrier wave with pulses having a frequency lower than that of the carrier wave, an antenna positioned before release of the missile to face a target, -a directional reilector on the antenna adapted to rotate at a predetermined frequency on an axis slightly offset with respect to the axis of symmetry, the antenna serving to transmit the pulses and receive echo pulses from said target, means including four channels for producing four signals 90 out of phase with one another, the received signals being introduced to the channels to produce output signals in the channels dependent on the position of the target with respect to the antenna, means for combining output signals of opposite phase to produce a pair of error signals, means for resolving the phase of the error signals to compensate forthe movement of the missile relative to the antenna, yand means for pivoting the missile relative to the antenna in accordance with the resolved error signals to correct any deviations in the direction of missile flight.

3. In combination in a seeker system for guiding a missile to intercept a target, means for forming a plurality of pulses recurring at a predetermined frequency, means triggered by the pulses to produce energy pulses having a carrier frequency, an antenna adapted to be trained on the target before flight and to revolve about the target during flight at a predetermined rate of rotation, the lantenna operating to beam the pulses to the target and to receive signals echoed from the target, means for discriminating between the pulses echoed from the target and pulses echoed from other objects located -at different distances along the antenna beam, means associated with 4the antenna for creating -a plurality of signals having a quadrature phase relationship with one another, means for mixing the received signals with each of the quadrature signals, means for combining the mixed signals of opposite phase to produce a pair of error signals having a quadrature relationship with each other, means for shifting the error signals by an angle determined by the rela- Ytive movement between the missile and the antenna, and means for utilizing the resolved error signals to pivot the missile relative to the antennaV for an adjustment of any error in direction during the flight of the missile towards the target.

4. In ycombination in a seeker system for guiding a missile to intercept a target, means for producing carrier signals modulated by pulses recurring at a predetermined frequency, an antenna for transmitting the pulse-modulated car'rier signals in a conical pattern revolving about a v,central axis at a predetermined rate, the antenna also receiving signals reflected from the target, means for detecting the signals received by the antenna, means for permitting only the pulses received from theY target to pass through the detector, means coupled to the antenna for producing a plurality of gate signals in quadrant relationship with one another, means for separately mixing the received pulses with each ofthe quadrant signals and 'for detecting the resultant signals, meanssfor combining the resultant signals of opposite phase and adjusting the phase of the combined signals in accordance with the angular relationship betweenV the missile and the antenna, means for differentiating the phase-adjusted signals, and servomechanisms operative in accordance with the differentiated signals to adiust the positioning of the missile relative to the antenna for a proper regulation of the direction of the missile llight towards the target.

5.. In combination in a seeker system for guiding a missile to intercept a target, means for producing carrier signals modulated by pulses recurring at a predetermined frequency, an antenna for transmitting the pulses in a conical pattern revolving about a central axis at a predetermined rate, the antenna also receiving signals reflected 4from the target, means for detecting the signals received by the antenna, means for permitting only the pulses received from the-target to pass through the detector, means coupled to the antenna for producing a plurality of gate signals in quadrant relationship with one another, means for separately mixing the received pulses with each of the quadrant signals and detecting the resultant signals, means for combining the resultant signals of opposite phase and resolving the phase of the combined signals by an angle corresponding tov that for-med by movement between the missile and the rellector in a predetermined plane, means for differentiating the resolved signals, means for combining the resolved vand differentiated signals, and servomechanisms operative by the combination of the differentiated and resolved signals to adjust the positioning of the missile relative to the antenna for a proper regulation of the direction of the missile flight towards the target. 6vr1 combination in a seeker system for guiding a missile to'intercept a target, means for producing a plurality of'pulses recurring at a predetermined frequency, means for producing carrier signals for the pulses, a directional antenna'adapted to rotate at a predetermined speed about an axis slightly displaced Y.from its pointing direction and to transmit pulse-modulated signals and receive signals reflected from the target, means for detecting and amplifying the received signals, means for gating the detecting and amplifying meansto operate only at the time that the pulse-modulatedsignals reflected from the target are being received, means associated with'the antenna for producing a plurality of signals 90 out of phase with one another, means for separately mixing each of these signals with the received signals, means for'cornbining resultant signals of opposite phase to produce aV pair of error signals, a pair of sine potentiometers for resolving the phase of the error signals in accordance with the angle of rotation between the missile and the antenna in a predetermined plane, meansl associatedwith each potentiometer for diterentiating the resolved signals and servomechanisms operative in accordance with the resolved and differentiated signals l2 to pivot the missile relative to the antenna for a proper adjustment of the course of the missile.

7. In combination in a seeker system for guiding a missile to intercept a target, an antenna, a reflector in the antenna, a first gifnbal in the antenna to provide a relative rotational movement between the missileI and the antenna in a first plane, a second gimbal in the antenna mounted on the first gimbal to provide a relative pivotal movement between the missile and the antenna in a'second plane substantially perpendicular to the first plane, means for rotating the missile relative to the first gimbal to maintain the pivotal movement ofthe missile relative to the second girnbal within predetermined limits, means for producing signals adapted to be directed by the antenna towards the target, means for acting upon the signals reflected from the-target to determine the position of the target relative to the missile, means for resolving the determination of target position in accordance with the angle of rotation of the missile relative to the first gimvbal, and means for altering the positioning of tne missile relative to the antenna in accordance with the resolved determination of target position to adjust the course of the missile for any errors in its flight towards the target.

8. In combination in a seeker system for guiding a missile on a collision course to intercept a target, an antenna pivotably mounted on the missile for pivotal movement of the missile relative to the antenna, the antenna being adapted to radiate pulses towards the target and to receive pulses reflected from the target, means for.

rotating the antenna at a predetermined frequency during the pulse radiations in a plane slightly skewed relative to the antenna, means operative upon the rotation of the antenna t0 produce a plurality of reference signals having a predetermined phase relationship to one another, means for combining the reflected pulses and the reference signals to produce a pair of error signals providing an indication of any deviation of the missile from the collision course, and means operative by the error signals to vary the positioning of the missile relative to the antenna for an adjustment' in the direction of the missile flight to the collision course, i

.9. In combination in a seeker system for guiding a missile on a collision course to intercept a target, an antenna pivotably mounted on the missile for pivotal movement of the missile relative to the antenna, the antenna being adapted to radiate pulses towards theI target and to receive pulses reflected from the target, means for rotating the antenna at a predetermined frequency during the pulse radiations in a plane slightly skewed relative to the antenna, means operative upon the rotation of the antenna to produce a plurality of reference signals having a predetermined phase relationship to one another, means for combining the reflected pulses and the reference signals to produce a pair of error signals producing an indication of any deviation of the missile from the collision course, means operative by the error signals to vary the positioning of the missile relative to the antenna for an adjustment in the direction of the missile ilight to the collision course, andmean's operative vin accordance with any relative movement between the antenna and the missile to adjust the phase and amplitude of subsequent error signals before any further variation in the positioning of the missile relative to the antenna.

References Cited in the tile of this patent UNITED STATES PATENTS 2,448,007 Ayres c Aug. 3l, 1948 2,512,693 Sparks June 27, 1950 2,557,401 Aging rune 19, 1951 2,594,317 Lancor Apr. 29, 1952 2,701,875 Baltzcr Feb. 8, 1955 

1. IN COMBINATION IN A SEEKER SYSTEM FOR GUIDING A MISSILE TO INTERCEPT A TARGET, MEANS FOR PRODUCING PULSES OF HIGH FREQUENCY ENERGY RECURRING AT A PREDETERMINED LOWER FREQUENCY, AN ANTENNA FOR BEAMING THESE PULSES TO A TARGET IN A REVOLVING PATTERN, THE ANTENNA ALSO SERVING TO RECEIVE THE SIGNALS REFLECTED FROM THE TARGET, MEANS INCLUDING FOUR GATED AMPLIFIERS FOR PRODUCING FOUR SIGNALS 90* OUT OF PHASE WITH ONE ANOTHER, THE RECEIVED SIGNALS BEING INTRODUCED TO THE AMPLIFIERS TO VARY THE OUTPUT OF THE AMPLIFIERS, MEANS FOR COMBINING THE OUTPUT AMPLIFIER SIGNALS OF OPPOSITE PHASE TO PRODUCE A PAIR OF ERROR SIGNALS 90* OUT OF PHASE WITH EACH OTHER, MEANS FOR SHIFTING THE PHASE OF THE ERROR SIGNALS TO COMPENSATE FOR MOVEMENTS OF THE MISSILE RELATIVE TO THE ANTENNA, AND MEANS FOR ADJUSTING THE POSITIONING OF THE MISSILE RELATIVE TO THE ANTENNA IN ACCORDANCE WITH THE PHASE SHIFTED ERROR SIGNALS TO CORRECT ANY DEVIATIONS IN THE FLIGHT OF THE MISSILE FROM A COLLISION COURSE TOWARDS THE TARGET. 